Non-invasive Demand Response Hot Water Recirculation Pump Signaling and Control Appliance

ABSTRACT

This invention provides demand activation of a hot water recirculation pump to reduce energy wasted from running the pump when its use is not needed. The invention uses momentary water flow at the remote tap as the signaling mechanism. Heated water flowing into the hot water egress pipe raises the temperature of the pipe. A temperature sensor continuously measures the temperature and provides the measurements to a controller where the time rate of change of temperature measurements are detected and used as the signal to operate the recirculation pump. Controller logic processes the digitized output of the temperature sensor, threshold detects the time rate of temperature change, and activates power to the external recirculation pump for timed intervals. This invention requires no modification to existing plumbing in a domestic plumbing system already equipped with a recirculation pump.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not Applicable

FEDERALLY SPONSORED RESEARCH

Not Applicable

BACKGROUND

1. Field

This application relates to hot water recirculation pump controls in domestic plumbing systems.

2. Prior Art

A domestic recirculating hot water system consists of a water heater, supply piping to deliver heated water to water taps in a building, return piping to return water from the taps to the water heater and an electric pump to circulate water flow from the water heater to the taps and then return the water back to the water heater. Circulating the water moves heated water close to each tap in the system such that; on opening the tap, very little water passes through the tap before heated water reaches the tap. The system provides two major benefits; convenience to the user and reduction of water wastage. Convenience results from a reduction in time required for heated water to reach a tap when it is opened. The shortened period of time that cold water is discarded down a drain while the user waits for heated water to reach the tap reduces wastage of water. There are energy costs from running the recirculation pump and from heat lost from the heated water in the supply and return piping. This invention reduces these energy costs by limiting the operation of the recirculation pump to periods when it is needed as determined by demand signaling from the user. The invention requires no additional signaling devices from the taps to the pump and no plumbing modifications to incorporate into an existing recirculation system. The invention uses water flow at the remote tap as the signaling mechanism and a temperature sensor and microcomputer control to operate the recirculation pump. There have been some approaches implemented and proposed for reducing the energy penalty of the hot water recirculation systems as follows:

-   -   1. Timer controlled pump. One commonly practiced technique for         reducing energy and cost penalties is to add a timer to control         the times of day that the pump will operate. The pump operating         is set to bracket potential usage intervals and, to ensure that         the pump is operating when needed, this typically means that the         pump is energized well before the actual need time and remains         energized well after. In addition, temporary changes in the         user's schedule are not always accommodated by the timer and         when the user requires hot water outside of the timer's active         period, the user must wait for heated water to flow from the hot         water heater to the tap while the unused cold water is         discarded.     -   2. Flow detection. U.S. Pat. No. 4,936,289 to Peterson proposes         that a flow detector in the cold water ingress side of a hot         water heater to signal a controller to activate the circulation         pump. This system uses a flow detection system that is inserted         into the plumbing system requiring a potentially costly         modification to the plumbing.     -   3. Push button demand activation. U.S. Pat. No. 4,201,518 to         Stevenson proposes that electrical push button switches be         installed at each hot water tap in the recirculation loop. The         switches are to be wired back to a pump controller that applies         power to the pump when signaled by a user pressing the button on         one of the switches. This system is a demand system that permits         a user to turn on the pump a short period of time before hot         water is to be drawn from the tap. The approach requires wiring         to be installed from each hot water tap to a controller located         close to the recirculation pump. The wiring would be difficult         and costly to add to a facility with pre-existing walls.     -   4. Pressure sensor. U.S. Pat. No. 4,142,515 issued to Skaats         proposes to install a pressure detector in the hot water egress         pipe leaving the hot water heater. The detector would sense the         pressure drop when a hot water tap is opened and this detection         would signal a controller to energize the recirculation pump for         a preset period of time. The system proposed has the advantage         that the pump is activated by sensing user demand transmitted         through the existing hot water supply lines and sensed as a         change in pressure at the hot water egress pipe from the water         heater. When used in an existing structure, the pressure switch         must be installed in existing plumbing requiring costly         modifications to the plumbing.     -   5. Light activation sensor. U.S. Pat. No. 7,036,520 B2 issued to         Pearson proposes to detect the activation of electrical lights         in proximity to a hot water tap and to use this detection to         activate the operation of a hot water recirculation pump. This         concept relies on electrical circuit installation in areas         relatively isolated to bathrooms, laundry rooms, kitchens, and         etcetera such that detection of electrical current in the         respective circuits will indicate human activity close to a hot         water tap. In addition, detection of this human activity close         to a hot water tap will be used as the signal to activate a hot         water recirculation pump. There are several problems with this         concept; electrical circuits are frequently not organized in         areas isolated to hot water usage areas, frequently humans in         areas with hot water taps do not energize lighting before using         hot water, many times humans do energize lighting and do not         intend to use hot water. In addition to these functional         limitations, the system requires modification to the electrical         circuits to install sensors that indicate usage of the circuits.

SUMMARY

This invention uses a temperature sensor mounted to the hot water egress pipe of a water heater to detect user hot water demand signaling. The user allows a small amount of water to momentarily flow from a hot water tap. This momentary flow allows hot water from the water heater to enter and warm the water heater egress pipe. The resulting temperature change of the pipe is detected by a sensor and electronics in a controller and interpreted as a user signal to start a recirculation pump. The controller applies power to the recirculation pump for a preset period of time to bring heated water to all of the taps in the recirculation system. The user signals the controller to start the pump by momentarily opening a hot water tap and then re-closing it. The user signals the controller a few minutes before hot water is required at the tap giving the pump sufficient time to start and circulate heated water to all of the taps in the water circuit. The operating time of the pump is limited by a timer in the controller to a period sufficient for heated water to reach all of the taps and for the user to begin drawing heated water from the tap.

DRAWINGS—FIGURES

FIG. 1 shows a typical hot water recirculation system that the invention is applicable for.

FIG. 2 shows the invention as it would be installed in the typical hot water recirculation system.

FIG. 3 shows a physical block diagram of the invention with sufficient detail to define all of its components and their functional relationships.

FIG. 4 shows a flow chart of the operational sequence and logic of the software in the invention.

DRAWINGS—REFERENCE NUMERALS Used in FIGS. 1, 2, 3

-   1. Water Heater -   2. Hot water egress pipe from the Water Heater -   3. Cold water ingress pipe into the Water Heater -   4. Hot water tap -   5. Hot water return from hot water tap -   6. Recirculation Pump -   7. Electrical power cable connecting the Controller to the power     mains -   8. Hot water recirculation loop return to the Water Heater -   9. Electrical power cable connecting the Controller to the Pump -   10. Temperature Sensor—integrated circuit that produces a voltage     proportional to temperature -   11. Controller Assembly—printed circuit board with components -   12. Cable connecting the Temperature Sensor to the Controller     Assembly Microprocessor—an integrated circuit -   13. Analog to Digital Converter—part of microprocessor -   14. Software program running in memory contained in the     microprocessor -   15. Run Timer—embedded peripheral in the microprocessor -   16. Hold Off Timer—embedded peripheral in the microprocessor -   17. Sample Timer—embedded peripheral in the microprocessor -   18. Microprocessor -   19. Parameter Selection Switches—switch bank used to select program     features -   20. AC Plug—connects the Controller to the alternating current (AC)     power mains -   21. AC Socket—connection point for the pump AC connector -   22. Relay—switches AC power to the AC socket and thus to the pump -   23. Power Supply—converts AC power to DC voltages for operating the     Controller circuitry.

Used in FIG. 4

-   S1. Initialize. Initializes all of the peripherals in the     microprocessor and gathers 16 digitized samples from the temperature     sensor. -   S2. Read Parameter Switches. Reads switches that set Sensitivity,     Run Time, and Hold Time. -   S3. Temperature Test. Compares the average of the 8 oldest     temperature samples to the 8 newest samples to determine if the     sensitivity threshold has been exceeded. -   S4. Start Run Time. Sets relay to start pump and initializes run     timer. -   S5. Run Time=End Test. Checks for completion of the pump run time. -   S6. Start Hold Time. Turns off pump and initializes Hold Off timer. -   S7. Hold Off Timer Test. Checks for completion of Hold Off Time. -   S8. Interrupt. A one second timer generates an interrupt. -   S9. Discard Oldest Sample. Oldest sample is discarded and newer     samples are shifted. -   S10. Take Newest Sample. A new temperature sample is digitized and     saved in the newest sample memory location. -   S11. Return to program. The interrupt service is complete, return to     the main program.

DETAILED DESCRIPTION

The following definitions and explanations are made to assist discussion:

-   -   1. Controller. This is an electronic control device that will         typically be collocated with an electric hot water recirculation         pump. The electric hot water recirculation pump is not part of         this invention.     -   2. Sensor. This is an electronic temperature sensor connected to         the Controller via a cable. The sensor will also be clamped to         the hot water egress pipe from a domestic hot water heater.     -   3. When referencing a component in one of the figures, the         component number will be bracketed in the text. For example, [1]         refers to the water heater in both figures.

Problem Description

Reference FIG. 1 during the following discussion. Many residences are equipped with a hot water recirculating electric pump [6] that recirculates water from the water heater [1] through a closed loop [2], [5], and [8]. The closed loop brings heated water close to a hot water tap [4] in the residence such that when the tap is opened, very little unheated water flows through the tap before heated water in the closed loop begins to flow through the tap. This system results in a reduction of water discarded into the drain while waiting for heated water to reach the tap and thus is a water saving device. In addition, since less user time is spent waiting for heated water to reach the tap, the device is a convenience to the user.

There is an energy penalty to be paid for the hot water recirculation system as heated water remains in the pipe distribution system for periods of time when hot water is not being used and thus increases heat loss in the system. In addition, the pump consumes electrical energy while operating.

In many residences the electric recirculation pump is operated continuously. In others, a clock timer is added that can be set so that the pump only operates during times of the day when hot water usage is expected. Both of these approaches to pump operation result in substantial energy wastage because the pump operates during times when heated water is not needed at the tap. Even with the timer, usage periods are projected when the timer is adjusted and generally exceed the actual time of hot water usage by a large margin.

Invention Description

This invention improves the hot water recirculation system by adding a sensor and controller that provides the following features:

-   -   1. The time of operation of the pump is reduced by using demand         signaling such that the pump starts on demand and continues         sufficiently long to bring heated water to the taps in the         recirculation system.     -   2. The pump controller and sensor are easily installed in an         existing hot water recirculation system. No plumbing         modifications are required to add the controller to an existing         recirculation system. Electrical modifications consist of simple         connection of the controller to the AC Mains, reconnection of         the pump from the AC Mains to the controller, and clamping a         temperature sensor to the hot water heater hot water egress         pipe.     -   3. The signaling system uses the water system as the signaling         media such that no wiring is required from the tap locations to         the pump controller.

Refer to FIG. 2 during the following description.

-   -   1. In the initial condition, the temperature of the water in the         water heater [1] is higher than in the hot water egress pipe [2]         and at the sensor [10]. The Controller [11] will monitor the         temperature measured by the sensor. The temperature at the         sensor will not increase appreciably unless heated water is         drawn into the hot water egress pipe.     -   2. A few minutes before the user desires hot water to be present         at a tap [4] the user momentarily opens any hot water tap and         then re-closes the tap. This action allows a small amount of         water to flow from the water heater [1] and into the hot water         egress pipe [2] toward the open tap.     -   3. The heated water causes the temperature to rise at the         temperature sensor [10]. The time rate of increase in         temperature is detected by the Controller [11] and used as a         signal to start the recirculation pump. The sensitivity of the         Controller to the time rate of change of temperature is         selectable to accommodate differences in systems.     -   4. When the Controller [11] detects that the time rate of change         of the temperature at the sensor exceeds the sensitivity         selection, the Controller switches power to the hot water         recirculation pump [6] and starts an internal run timer which         determines the length of time that the pump will operate. The         length of time that the run timer and pump are on is selectable         to accommodate differences in system installations.     -   5. The pump [6] circulates heated water from the Water Heater         [1] to the tap [4] and back to the water heater for the period         of time determined by the Controller [11] internal run timer.     -   6. The user opens the tap [4] to use the heated water.     -   7. The Controller [11] reaches the preselected internal run time         limit and disconnects power from the pump [6]. The pump ceases         operation. Once heated water has been brought from the Water         Heater [1] to the tap [4], the user may continue to draw heated         water from the system without operating the pump.     -   8. An additional internal hold off timer in the Controller [11]         prevents the Controller from restarting the pump [6] for a user         selectable time period after the pump has been turned off by the         Controller. The internal hold off timer prevents any continued         temperature increase at the sensor [10] from causing the         Controller to restart the pump while heated water is being used         at the tap [4]. The hold off time interval is selectable to         accommodate differences in system installations.     -   9. The user will continue to draw heated water from the tap. The         temperature of the hot water egress pipe [2] will continue to         increase but at a diminishing rate until the time rate of         temperature increase at the sensor [3] is less than the         Controller sensitivity selection. The internal hold off time is         greater than the time required for the time rate of change of         the temperature at the sensor to decline below the Controller         sensitivity selection.     -   10. When the internal hold off time is reached, the Controller         [11] will resume measurement of the time rate of change of the         temperature at the sensor [10]. While the user continues to draw         heated water from the tap. However, the sensitivity threshold         will not be exceeded and the Controller will not apply power to         the pump [6].     -   11. When the user has completed drawing heated water from the         tap [4] and closed the tap, the temperature of the water in the         hot water egress pipe [2] will decline until it is sufficiently         reduced to return to the initial condition described in item 1.

The resulting advantages to the user are:

-   -   1. Minimal water is wasted by discarding water waiting for         heated water to arrive at the tap. Only a small amount of water         is discarded when the user opens the tap to signal the         controller to apply power to the pump.     -   2. The recirculation pump operates for a short period of time         beginning shortly prior to usage of heated water at the tap and         continuing for a user selectable time period.     -   3. The user has the convenience of always having hot water at         the tap when usage is desired. This can be particularly         important when a user's schedule change places the user's demand         for heated water at the tap outside of a time window defined by         a clock timer.     -   4. The pump only operates on demand and energy lost from running         the electric pump is minimized.     -   5. Heated water is only conveyed into the pipe on demand and         energy lost from maintaining heated water in the piping system         is minimized.     -   6. The invention is intentionally designed for simplified         installation. A single temperature sensor is clamped to the hot         water pipe exiting the heater and the pump is electrically         connected to the controller. The controller is connected to the         power mains. No modification of plumbing is required for         installation.

Key Technologies Employed

Refer to FIG. 3 during the following discussion. The Controller and Temperature Sensor are electronic devices connected with a cable that supplies power to the Temperature Sensor from the Controller and returns a voltage proportional to the temperature back to the Controller.

-   -   1. The Temperature Sensor [10] is an integrated circuit         incorporating a sensing element and amplifiers as needed to         deliver a voltage to the controller. The Temperature Sensor         voltage closely approximates the temperature by a linear         equation.     -   2. The Temperature Sensor [10] and the Controller [11]         electronics are powered by a power supply [23] on the Controller         circuit card that converts mains power [20] to direct current         power conditioned for operating the electronics.     -   3. An analog to digital (A/D ) conversion circuit [13] on the         Controller [11] converts the voltage from the Temperature Sensor         [10] into digital samples. The A/D converter can be internal to         the sensor or included in circuitry in the Controller as shown         in FIG. 3.     -   4. The Controller [11] contains a microprocessor [18] that         receives the digital samples from the analog to digital         converter [13] and processes them with software [14] to         determine the time rate of change of the temperature measured by         the Temperature Sensor [10].     -   5. Timers internal to the microcomputer [18] are used to measure         the run [15] and hold off [16] times. Another timer is used to         determine the sample rate for the analog to digital converter         [17].     -   6. A relay [22] on the Controller [11] circuit card switches         power to the pump under control of the microcomputer [18] and         software [14]. The pump connects to the Controller circuit card         at the AC socket [21].     -   7. A bank of switches [19] on the Controller circuit card is         used to select operating parameters including the temperature         time rate of change sensitivity threshold, pump run time, and         pump hold off time.

Computer software [14] averages the first n samples and the last n samples from the analog to digital converter [13] to produce two values, the newest average and the oldest average. Averaging reduces random noise and increases digital precision. Subtracting the newer average from the older average determines the amount of temperature change that has occurred between the two average intervals. The last 2n samples are processed. N is chosen based upon the capabilities of the processor, the sample rate, the computational latency, and the digital precision needed. Sampling at one sample per second with a 12 bit analog to digital converter and using n=8 produces reliable detection, low probability of false detection, and reasonable detection latency.

When the newest average is greater than the oldest average by an amount that exceeds the sensitivity threshold, the controller detects that a flow of hot water has entered the water heater egress pipe and this is interpreted as a signal to start the operation of the recirculation pump. The microprocessor [18] then activates a relay [22] which switches power to the pump. The controller will activate the relay for a period of time determined by the Run Timer [15] which is sufficient to allow the pump to convey hot water to all of the taps in the recirculation loop and for the user to begin to use hot water from the tap. When the time interval defined by the Run Timer elapses, the microprocessor will deactivate the relay and stop pump operation.

After deactivation, the relay will be held in the deactivated condition for a period of time defined by the Hold Off Timer [16]. The Hold Off Time is sufficient for the temperature in the hot water egress pipe to approach the maximum temperature. At completion of the Hold Off time interval, temperature increases at the sensor will be small and will not exceed the sensitivity threshold used to activate pump operation. The relay and pump will remain deactivated until the user has closed the tap, water temperature in the egress pipe has cooled, and the controller is again signaled by momentary opening of a hot water tap. 

1. Temperature change in the egress pipe of a water heater is measured by a sensor and used as the signaling mechanism for activating a hot water recirculation pump.
 2. The said temperature change measured by said sensor is used as the input to logic in a controller.
 3. The said controller controls the operation of the said water recirculation pump by applying or disconnecting power to the pump.
 4. The said logic in the said controller determines operation time of the said water recirculation pump. 